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<h1><a href="https://archiveofourown.org/works/28016937">We go together like black and gold</a> by <a class='authorlink' href='https://archiveofourown.org/users/Osamuskittycat/pseuds/Osamuskittycat'>Osamuskittycat</a></h1>

<table class="full">

<tr><td><b>Series:</b></td><td>Boywife Osamu AU [1]</td></tr>

<tr><td><b>Category:</b></td><td>Haikyuu!!</td></tr>

<tr><td><b>Genre:</b></td><td>Age Difference, Incest, M/M, Sibling Incest, camboy osamu, miyacest, older Atsumu</td></tr>

<tr><td><b>Language:</b></td><td>English</td></tr>

<tr><td><b>Status:</b></td><td>Completed</td></tr>

<tr><td><b>Published:</b></td><td>2020-12-11</td></tr>

<tr><td><b>Updated:</b></td><td>2020-12-11</td></tr>

<tr><td><b>Packaged:</b></td><td>2021-05-10 21:28:53</td></tr>

<tr><td><b>Rating:</b></td><td>Explicit</td></tr>

<tr><td><b>Warnings:</b></td><td>Underage</td></tr>

<tr><td><b>Chapters:</b></td><td>1</td></tr>

<tr><td><b>Words:</b></td><td>3,322</td></tr>

<tr><td><b>Publisher:</b></td><td>archiveofourown.org</td></tr>

<tr><td><b>Story URL:</b></td><td>https://archiveofourown.org/works/28016937</td></tr>

<tr><td><b>Author URL:</b></td><td>https://archiveofourown.org/users/Osamuskittycat/pseuds/Osamuskittycat</td></tr>

<tr><td><b>Summary:</b></td><td><div class="userstuff">
              <p>It’s all Oikawa’s fault. Because almost anything that causes a downhill spiral starts with that stupid pretty boy, just ask Iwaizumi.</p>
            </div></td></tr>

<tr><td><b>Relationships:</b></td><td>Miya Atsumu/Miya Osamu</td></tr>

<tr><td><b>Series:</b></td><td>Boywife Osamu AU [1]</td></tr>

<tr><td><b>Series URL:</b></td><td>https://archiveofourown.org/series/2077527</td></tr>

<tr><td><b>Comments:</b></td><td>16</td></tr>

<tr><td><b>Kudos:</b></td><td>277</td></tr>

</table>

<a name="section0001"><h2>We go together like black and gold</h2></a>
<div class="story"><div class="fff_chapter_notes fff_head_notes"><b>Author's Note:</b><blockquote class="userstuff">
      <p>There’s a significant amount of age difference between them so keep that in mind</p>
    </blockquote></div><div class="userstuff module">
    
    <p>It’s all Oikawa’s fault. Because almost anything that causes a downhill spiral starts with that stupid pretty boy, just ask Iwaizumi.</p>
<p> </p>
<p>Atsumu doesn’t know how he got roped into being in a group FaceTime call with Oikawa Tooru of all people. It’s honestly all Shouyou-kun’s fault, that boy seemed to want all of his friends to be friends with each other.</p>
<p> </p>
<p>“Someone please take Oikawa’s phone from him.”</p>
<p> </p>
<p>“Don’t be a grump, Miya! I’m being serious!” </p>
<p> </p>
<p>“There’s not a chance that there are random people out there on the internet getting off while wearing a fuckin’ jersey”</p>
<p> </p>
<p>Oikawa scoffs &amp; Atsumu can see the moment Iwazumi contemplates taking a one way flight to Argentina to punch his best friend and honestly, Atsumu is two seconds away from joining him because this whole conversation is absolutely ridiculous even by Oikawa’s standards.</p>
<p> </p>
<p>“There are! Me and the guys found two videos last week!”</p>
<p> </p>
<p>“I’m too tired for this shit. See you fuckers later.”</p>
<p> </p>
<p>Atsumu hangs up before Oikawa can demand his attention but not five minutes later a text pops up on his screen from the setter. </p>
<p> </p>
<p>‘Here’s a link to a video made just for you, Miya-san 🤗 enjoy!’</p>
<p> </p>
<p>Before Atsumu swipes out of the chat he notices that in the thumbnail the jersey really is a Jackals jersey, Atsumu’s number 13 plastered right on the front. </p>
<p> </p>
<p>“The fucker wasn’t lyin’...”</p>
<p> </p>
<p>Atsumu shouldn’t click on the video giving Oikawa any form of satisfaction was almost enough to kill his curiosity but what Oikawa didn’t know, wouldn’t feed his ego. </p>
<p> </p>
<p>The guy in the video looks young despite the fact that Atsumu can’t see his face, the only visible thing beside the jersey is the pale thighs that are shaking as the guy seems to be rocking down against what Atsumu can only assume is a dildo. </p>
<p> </p>
<p>The guy seems to be enjoying himself, breathy little moans that send a shiver down Atsumu’s spine as he watches the guy’s movements pick up speed, a hand moving away from the floor to lift the bottom of the jersey up to expose his tiny cock to the audience, whining softly once he bring the jersey high enough to his nose. </p>
<p> </p>
<p>Atsumu maxes up volume, so hypnotized by the wet little cock and broken whimpers that he almost misses the barely audible ‘Sumu-nii’ that slips through his headphones, ultimately breaking Atsumu’s last bit of sanity. </p>
<p> </p>
<p>Only one person has ever call him ‘Sumu-nii’ and that person was far too young to be posting things like this on the fucking internet. The same person who Atsumu had practically raised himself, who he loved more than volleyball and who he would be seeing in less than 24 hours. </p>
<p> </p>
<p>Atsumu had to repeat that bit of the video a good ten times before he came to terms with the fact that the voice definitely belonged to one person and one person only:</p>
<p> </p>
<p>His baby brother Osamu. </p>
<p> </p>
<p>—</p>
<p> </p>
<p>The next day Atsumu stands in front of his parents house with a million thoughts racing through his head, refusing to let him sleep the night before. </p>
<p> </p>
<p>Atsumu wanted so desperately to believe that the guy in the video wasn’t Osamu but he’d replayed the video enough times to have it memorized frame for frame. </p>
<p> </p>
<p>His baby brother had filmed not just one video but multiple videos of him riding a dildo (how he got that, Atsumu really didn’t want to know) while sniffing Atsumu’s jersey, as if wishing his big brother was there with him.</p>
<p> </p>
<p>Atsumu was going to hell and he was taking his little brother with him.</p>
<p> </p>
<p>“SUMU-NII!”</p>
<p> </p>
<p>The force of his little brother crashing into his chest and the lack of sleep cause Atsumu to stumble back, falling right onto his ass and ending up with a lap full of Osamu, who grins widely at his big brother from his perch on the elders lap. </p>
<p> </p>
<p>“You’re finally home!”</p>
<p> </p>
<p>Atsumu tries his hardest to smile at his baby brother, forcing the memory of the video into the back of his mind as he allows Osamu to wrap him up in a hug, face buried against Atsumu’s neck. </p>
<p> </p>
<p>“Y-Yeah, I’m home.”</p>
<p> </p>
<p>Osamu’s smile when he pulls back does nothing to stop the way his heart is about to shake out of his chest, mind replaying the video over and over until Atsumu can’t stare at his little brother anymore. </p>
<p> </p>
<p>“Come on, ‘Samu. Let’s go see mom and dad.”</p>
<p> </p>
<p>Atsumu desperately tries not to crumble when Osamu pouts up at him, his fourteen year old little brother shouldn’t hold so much power over him, especially when all Atsumu can think about is the way Osamu whimpered his name as he came with Atsumu’s jersey pressed to his face. </p>
<p> </p>
<p>“Are you okay, Sumu-nii? You look really tired.”</p>
<p> </p>
<p>Atsumu cracks a small smile as he pats Osamu’s head as he gets up off the floor, reaching down to help his little brother up too. </p>
<p> </p>
<p>“I’ll be okay...just a rough practice that’s all.”</p>
<p> </p>
<p>Osamu nods quietly as he takes Atsumu’s hand to lead him back towards the house. </p>
<p> </p>
<p>“Did you bring me the new Jackals jersey? You promised I could have the one they gave you.”</p>
<p> </p>
<p>Atsumu shakes his head as reaches into his duffle to pull the jersey out, forgetting momentarily about everything that’s been haunting him as he throws his brother the jersey. </p>
<p> </p>
<p>“Yeah, yeah. Here you go, ‘Samu.”</p>
<p> </p>
<p>It’s not until Atsumu looks back at his brother, watching the way Osamu lifts the jersey up to his face as he hugs it close that the figurative bucket of ice water drops onto his head.</p>
<p> </p>
<p>All the times Osamu had stolen one of Atsumu’s Jackals jerseys when he came home to visit, now makes sense and Atsumu can’t believe he’s been feeding his brother’s addiction without realizing it. </p>
<p> </p>
<p>Osamu wanted Atsumu and somehow, against his better judgment, Atsumu wanted him too.</p>
<p> </p>
<p>—</p>
<p> </p>
<p>Dinner that night is absolute torture for Atsumu, who spends entire thing with Osamu sitting on his lap while wearing the jersey that Atsumu brought for him, a sight that is actually normal to see in the Miya household. </p>
<p> </p>
<p>Ever since Osamu was born his favorite person was Atsumu and that never changed as the boy got older, their parents always joked that whoever Atsumu ended up with would have to compete with Osamu for Atsumu’s affection because Osamu was Atsumu’s favorite person and would do just about anything to keep his baby brother happy. </p>
<p> </p>
<p>Now Atsumu has to wonder where he went wrong and his love for his little brother caused Osamu to become sexually attracted to him, a thought Atsumu had never imagined happening at any point in his life. But now as he sits in the living room trying to watch tv with their dad, Osamu curled up snuggly in his lap with his face tucked under Atsumu’s chin, he figures it wouldn’t be completely horrible to give into the new desires burning up inside of him.</p>
<p> </p>
<p>With a kiss to the top of Osamu’s head Atsumu pulls him closer, hiding his grin in Osamu’s hair as he makes plans to finally give his little brother exactly what they both want. </p>
<p> </p>
<p>Atsumu really can’t wait for their parents to fall asleep so he can put his plan into motion, Osamu will be his in more ways than one once the night is over.</p>
<p> </p>
<p>—</p>
<p> </p>
<p>That night once their parents are finally asleep, Atsumu slips out of his room and tip toes his way down the hall to Osamu’s room, his brother having snuck away an hour before everyone else, claiming that he was really sleepy.</p>
<p> </p>
<p>Atsumu had hugged his little brother close, kissing the top of his head before allowing the blushing boy to race up to his room after gently patting him on the butt, “Sleep tight, baby boy.”</p>
<p> </p>
<p>There’s a soft noise coming from Osamu’s room when Atsumu carefully leans against the door with his ear pressed against the wood, he needs to be careful and try his hardest to not spook his little brother or worse, make his Samu think that Atsumu doesn’t feel the same that he does.</p>
<p> </p>
<p>With a deep breath, Atsumu lifts a hand to wrap around the door handle before slowly pulling it down so that it doesn’t make any noise as he pushes the door open. </p>
<p> </p>
<p>Once inside of the room a few things happen in quick session:</p>
<p> </p>
<p>Firstly, Atsumu gets a front row seat to the sight of Osamu wearing his jersey, dildo resting next to his hip while he fingers himself open for it. </p>
<p> </p>
<p>Secondly, Osamu lets out a terrified squeak the moment he catches sight of his older brother standing by the door, quickly scrambling under the blankets with a terrified squeak. </p>
<p> </p>
<p>Lastly, Atsumu’s heart almost breaks when he hears Osamu’s panicked breathing pick up in volume his little brother’s body shaking with every whimper. </p>
<p> </p>
<p>“Samu...Baby boy...” Atsumu’s soothing words do nothing to help calm his scared little brother, who refuses to release his grip on the blanket no matter how hard Atsumu tries. </p>
<p> </p>
<p>“G-Go away...P-Please just go away...”</p>
<p> </p>
<p>Atsumu almost listens to him, but he didn’t come here to be a coward so he uses his larger body to pin Osamu down with his legs on either side of his brother before gripping the blanket to pull it away from Osamu’s face. </p>
<p> </p>
<p>The moment Atsumu sees the tear streaked cheeks his heart breaks, a frown pulling on his lips as he reaches a hand out to gently cup Osamu’s cheek, thumb brushing away his tears as best as he can. “Please don’t cry, Baby boy...I promise I’m not mad.”</p>
<p> </p>
<p>Osamu’s eyes are full of confusion and fear as he sniffles quietly, leaning into Atsumu’s touch despite everything going on. </p>
<p> </p>
<p>“Y-You’re not m-mad at me..?” </p>
<p> </p>
<p>Atsumu smiles softly as he leans down to press a soft kiss to Osamu’s forehead, heart bursting with love for his baby brother when he sees the tiny smile on his lips. </p>
<p> </p>
<p>“Of course not. How could I be mad at such a beautiful boy dressed up in my jersey, at least now I get to see how good you look up close and personal instead of watching you through a computer screen.”</p>
<p> </p>
<p>Osamu’s eyes widen at Atsumu’s words, cheeks flushed as he stares up at his brother in surprise. “Y-You saw my videos? I-I can explain-“ </p>
<p> </p>
<p>Before Osamu can even try explaining himself, Atsumu leans down and claims the younger boy’s lips in a kiss that leaves both of them breathless and Atsumu hard in his sleep pants. </p>
<p> </p>
<p>“I’m not mad about the videos. I’m mad that all those random people on the internet got to see my sweet little Samu dressed up in my jersey, fucking himself silly and I didn’t.” Atsumu’s thumb brushes across Osamu’s bottom lip, grinning at the way his little brother’s mouth drops open to suckle on the digit, “Fuck. Look at that slutty little mouth just begging for me to put my cock in it.” </p>
<p> </p>
<p>The sound that comes out of Osamu makes something primal come alive inside of Atsumu, who throws the blanket off his little brother to expose the sight of his milky thighs and the little tent his tiny cock makes beneath Atsumu’s jersey, “Fuck...My little Samu is the most beautiful thing I’ve ever seen in my life.” </p>
<p> </p>
<p>Atsumu leans down to brush his lips against Osamu’s throat as he slips a hand up the jersey to fondle his brother’s little cock, smirking at the broken whimper that slips out. “You’re so tiny, baby boy...I could use you as my own personal cock sleeve if I wanted to.” </p>
<p> </p>
<p>Osamu’s broken cry of “P-Please, Sumu-nii!” Makes Atsumu’s cock twitch in his pants as he sits back to stare down at his flushed and whimpering brother, who lifts the collar of the jersey higher to breathe in Atsumu’s scent all while exposing more of his milky skin for Atsumu’s greedy eyes to enjoy, “I knew you’d love being Sumu-nii’s personal cock sleeve, such a good little slut” </p>
<p> </p>
<p>Osamu blushes brightly as he pulls the jersey up higher until it’s at his hips, setting his feet on the bed before he spreads his legs so that his big brother gets full view of his tiny wet and obviously stretched hole, “Want to make Sumu-nii feel good. Want Sumu-nii to give me his...his c-cum...” </p>
<p> </p>
<p>Atsumu silently thanks every deity that gave him this absolute vixen of a boy as a little brother while he moves to stand from the bed, shushing Osamu softly when he whines for his brother with outstretched hands, “Relax, baby boy. I’m just taking my pants off.”</p>
<p> </p>
<p>The pout on Osamu’s lips makes Atsumu want to swoop in and kiss it away but he forces himself to focus. They’ve got the whole night ahead of them to do everything and anything.</p>
<p> </p>
<p>Atsumu can’t wait to show his little brother how much better Sumu-nii’s cock is compared to that dildo of his. </p>
<p> </p>
<p>—</p>
<p> </p>
<p>“S-Sumu-nii! P-Please!” </p>
<p> </p>
<p>With a soft coo, Atsumu brushes a hand along Osamu’s thigh as he presses his fingers up against that sweet spot inside of his little brother, smirking at the way Osamu whines softly while rocking down against his brother’s hand, “Such a needy little baby, any louder and our parents might hear you. Do you want them to hear how much of a little slut you are for Sumu-nii?”</p>
<p> </p>
<p>Osamu whimpers softly while mouthing at the collar of Atsumu’s jersey as he lets his big brother manhandle him until he’s sat in Atsumu’s lap, who presses a soft kiss to Osamu’s forehead while keeping three fingers pressed up inside of him, “Such a good boy for Sumu-nii, wish I could take you back to my place and keep you there all the time. Would you like that, Samu? Wanna be Sumu-nii’s little wife?”</p>
<p> </p>
<p>Quivering lips brush against Atsumu’s as Osamu grips his shoulders while rocking down against the fingers pressed up deep inside of him, tiny little cock leaving a wet spot on the front of Atsumu’s jersey, “I-I wanna be Sumu-nii’s w-wife...I’d be s-such a good w-wife for Sumu-nii! The bestest o-one ever!”</p>
<p> </p>
<p>Atsumu’s cock twitches at the image his brain provides him of Osamu in an apron and dress, waiting for his Sumu-nii at the door to take his duffle and kiss him hello before leading him to the table so that they can enjoy a meal together like a real husband and wife would, “I know you would be, Baby. I can just imagine how beautiful you’d look all dressed up for me when I’d come home from practice. The most beautiful wife in the world.”</p>
<p> </p>
<p>The broken whine that slips out of Osamu as Atsumu removes his fingers causes the elder boy to chuckle softly as he presses his lips to Osamu’s softly while he leans back against the wall, keeping his little brother pressed close to his chest, “Gonna be a good boy and ride Sumu-nii, Baby boy? Ride me so good until I fill your little hole up with all of my cum, show you just how much better than your little toy Sumu-nii’s cock is.”</p>
<p> </p>
<p>Osamu nods quickly as he moves to pull the jerseys off but Atsumu’s hand on one his own stops him instantly, looking up at his big brother, who smiles softly while helping Osamu lower the jersey back down.</p>
<p> </p>
<p>“I love how you look in my jersey, Baby. All those people who watch your videos know exactly who their star belongs to. I’m the only one allowed to touch you. Right, ‘Samu?”</p>
<p> </p>
<p>The dazed look in Osamu’s eyes sets a fire off in Atsumu’s chest as he slowly lifts his little brother up, a hand curling around his cock to help Osamu rest the head against his stretched hole, “I-I’m only Sumu-nii’s c-cocksleeve...his little wife...I l-love my Sumu-nii!”</p>
<p> </p>
<p>The end of Osamu’s words break off into a high whine that Atsumu doesn’t bother to muffle as his head spins at how tight his little brother is, whose eyes have rolled back as he grips onto Atsumu’s shirt like a lifeline while his body opens up for his big brother’s thick cock that stretches him out beyond his limits. </p>
<p> </p>
<p>Definitely ten times better than his pathetic little toy. </p>
<p> </p>
<p>Once Osamu’s ass is flush with Atsumu’s lap, he lets out a breathless giggle as he lifts the bottom of the jersey to show off the cum splattered across his stomach to a wide eyed Atsumu, who can’t believe his little brother just came from Atsumu’s cock sliding into him. </p>
<p> </p>
<p>“Baby...I can’t believe you came just from Sumu-nii putting his cock inside of you, such a good little slut.”</p>
<p> </p>
<p>Osamu watches wide eyed as Atsumu scoops up some of the cum off of his belly before lifting the fingers up to his brother’s mouth with a sharp grin on his lips, “Clean up your mess like a good boy, ‘Samu.”</p>
<p> </p>
<p>Atsumu feels his soul descend to a whole new world as he watches Osamu’s pretty pink lips wrap around his fingers, sucking the cum right off of Atsumu’s fingers as he slowly starts to move his body up and down his older brother’s cock, eyes fluttering as he picks up a rhythm that he likes. </p>
<p> </p>
<p>The only sounds in the room are their labored breathing and the wet noises coming from Atsumu’s cock sliding in and out of his baby brother’s hole, that flutters around him when he moves a hand from Osamu’s hip to wrap around his tiny cock, smirking when it gives a weak twitch in his hand.</p>
<p> </p>
<p>“I can’t wait to see you come with Sumu-nii’s cock in your slutty little hole, such an amazing cocksleeve for me. I can’t wait to show you all the fun ways Sumu-nii is gonna fuck this slutty little hole, watch my cum drip down your ruined hole before I plug it all back inside of you.”</p>
<p> </p>
<p>Osamu has to muffle his cries of pleasure against Atsumu’s neck, the vibrations spurring the elder on to fuck up harder and faster into the young boy on top of him, “You’re gonna be a good boy and take all of Sumu-nii’s cum, right? Gonna let me fill up your little hole until it can’t take anymore because you’re such a good boy, ‘Samu.”</p>
<p> </p>
<p>When Osamu comes for a second time that night, his hole clenches around Atsumu’s cock, causing the elder to fuck up into his brother a few times in quick session before he holds Osamu flush against him as he keeps his promise of filling his little brother’s hole with his cum. </p>
<p> </p>
<p>The jersey on Osamu is absolutely ruined now, painted with the younger’ cum and Atsumu isn’t the slightest bit upset by it because there’s nothing more beautiful than his fucked out baby brother covered in both of their cum, smiling sweetly up at him.  </p>
<p> </p>
<p>“D-Did I do good, Sumu-nii…?”</p>
<p> </p>
<p>Atsumu rests his fingers under Osamu’s chin to lift the boy’s head up to claim those beautiful lips in a kiss that makes the younger boy’s toes curl and a soft whine to slip out of his mouth and straight into his Sumu-nii’s, “You absolutely blew my mind, Baby. Such an amazing boy for Sumu-nii.”</p>
<p> </p>
<p>When Atsumu finally finishes cleaning up and has changed Osamu into clean clothes, he pulls his sleeping baby brother close and thinks about how he’s going to convince their parents to let Osamu live with him under the guise that there’s a better school where he lives and that they deserve to ‘live their lives’. </p>
<p> </p>
<p>It’s a plan that he won’t rest until it pulls through but for now he just pulls Osamu closer and presses a soft kiss to his forehead before closing his eyes and settling down for the night. </p>
<p> </p>
<p>Atsumu already has Osamu as his for now and for forever, everything else will fall into place eventually. </p>
  </div><div class="fff_chapter_notes fff_foot_notes"><b>Author's Note:</b><blockquote class="userstuff"><p>My Twitter for more Miyacest @osamuskittycat</p></blockquote></div></div>
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